SANTA ELENA, Venezuela, July 1 (Reuters) - President HugoChavez defied his health problems to join a massive rally whileopposition rival Henrique Capriles took to the remotest cornersof Venezuela at Sunday's formal launch of the presidential race.

Unable to repeat the frenetic campaigning of past electionsdue to his struggle with cancer, a fist-pumping Chaveznevertheless made a rare appearance at a rally in centralVenezuela to underline he is fit enough for the Oct. 7 vote.

Capriles, a young state governor seeking to end 13 years ofsocialist rule in the South American OPEC member, flew to twodistant spots near the Brazilian and Colombian borders tohighlight alleged government neglect of remote communities.

Chavez has a two-digit lead in most polls, but there is alarge percentage of undecided voters and one respected localpollster this week put the pair head-to-head.

After three operations to remove two malignant tumors duringa year-long battle with cancer, the ever-upbeat Chavez, 57, hasin recent weeks declared himself in full recovery and his energylevels appear to be surging.

"My God, give us health and life to lead this people tovictory!" he tweeted before riding on the top of a truck throughstreets lined with thousands of ecstatic supporters.

Most analysts agree the vote is shaping into Venezuela'sclosest since Chavez took power in 1999, turning himself intoone of the world's best-known and controversial leaders with hisanti-American rhetoric and radical nationalization policies.

CAPRILES CROSSES COUNTRY

Miranda state governor Capriles - a center-left politicianwho admires Brazil's mix of free-market economics with strongwelfare policies - is widely considered the opposition's besthope after being outwitted for years by the wily Chavez.

His dash from the capital Caracas to the remote southeasterncommunity of Santa Elena, then across to La Guajira village onthe western border near the Caribbean, was part of an oppositionstrategy to highlight the 39-year-old's energy and youth incontrast with the ailing Chavez.

"My commitment is to reach the most forgotten people," hesaid in a speech to a small group of indigenous inhabitants inSanta Elena, close to the majestic, flat-topped Roraima mountainin a vast and barely populated region near Brazil.

"Over there nearby is Brazil. Its government understood howto work. Brazil has taken off. Now it's Venezuela's turn."

Though Venezuela's opposition is more united than everagainst Chavez, Capriles still faces a formidable task toovercome the president's unique rapport with the poor and vastspending power thanks to vast oil revenues.

Wearing his trademark red military beret, Chavez blewkisses, clapped, laughed and waved as he rode through thecrowds. He still, however, looked bloated and overweight fromthe effects of his cancer treatment and heavy medication.

Unusually, state media, where Capriles is normally onlymentioned in insults, covered some of his activities on Sunday.At one point, a split screen showed the rival rallies under thecaptions "Candidate of the Fatherland" for Chavez and "Candidateof the Right" for Capriles.

Chavez's ministers lined up to call Capriles a "loser" andpuppet of capitalism who would dismantle the popular missionsChavez has set up to provide free education, health services andsubsidized food in poor areas.

"Chavez's whole heart is open to the people," said GirolamoAmbla, 43, dressed in the red colors of Chavez's Socialist Partyand clutching a doll of the president as hundreds of supporterswaited for him to appear at the town of Mariara.

Government supporters held parties and vigils acrossVenezuela overnight, while the opposition organized scores ofpro-Capriles caravans around the nation on Sunday.

"While the other candidate uses the TV, we will stay in thestreet," Capriles' campaign head Armando Briquet said, referringto Chavez's forcing of all terrestrial TV channels to broadcastmany of his speeches and appearances live.